The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.
The interference-limited nature of CDMA systems results from the receiver design: reception is typically based on a spreading code matched filter (MF) or a correlator. Since the received spreading codes are usually not completely orthogonal, multiple access interference (MAI) is present in the receiver.
Sub-optimal multi-user receivers have been developed for fighting multiple access interference. Multi-user receivers can be categorized in several ways, where one is to classify the receivers to two main classes: linear equalizer and subtractive interference cancellation (IC) receivers. Linear equalizers, for example zero-forcing (ZF), de-correlating detectors or minimum mean square error (MMSE) detectors, are linear filters suppressing multiple access interference. The principle of an IC receiver is that the multiple access interference component is estimated, and then subtracted from the received signal for making decisions more reliable. Multiple access interference cancellation can be carried out by using serial interference cancellation (SIC) detectors.
Multiple-input and multiple-output (MIMO) refers to systems using multiple antennas both at a transmitter and receiver to improve the performance of radio communication systems.
A conventional channel decoder aided SIC detector detects MIMO data streams successively. Because of a channel decoding delay, the SIC detector buffers received signal samples, corresponding channel and noise variance or noise covariance estimates, which demands large signal buffers.